This invention relates to tires having treads which contain only a minimal amount, if any, of carbon black reinforcement, which are substantially silica reinforced and which thereby have a relatively low electrical conductivity. Accordingly a path of electrical conductivity is desired through such tread to a ground-contacting portion of the tread in order to dissipate static electricity from the tire to the ground.
Tire treads are often provided as a rubber cap/base construction in which the tread cap layer has an outer running surface designed to be ground contacting and the usually softer supportive tread base layer underlies the tread cap layer and is not intended to be ground contacting. The rubber of the tread base is usually reinforced with a significant amount of carbon black and with a minimal amount, if any, of silica reinforcement and is thereby considerably more electrically conductive than a silica reinforced rubber tread cap layer which contains only a minimal amount, if any, of carbon black reinforcement.
It has heretofore been proposed to provide path of reduced electrical conductivity through a tire tread cap layer of a relatively non electrical conductive rubber composition by providing a thin, relatively electrically conductive, continuously straight shaped rubber strip extending as a part of an electrically conductive tread base through the tread cap layer to its running surface. For example, see U.S. Pat. No. 5,942,069 and European Patent Publication Nos. EP0681931, EP0747243, EP0812710 and EP0847880.
However, such heretofore described electrically conductive rubber strips are seen herein to simply extend directly through the relatively electrically nonconductive tread cap in a basically a straight configuration.
In practice, where the electrically conductive strip extending through the tread is of a rubber composition having a significantly lower modulus than the rubber composition of the tread cap, lateral stability of the tire tread may be somewhat weakened. In particular, where the softer rubber strip divides the tread blocks, or segments, through which the rubber extends and divides into at least two sub-parts with the softer rubber strip therebetween, lateral stability of the tire tread and thereby the handling of the tire might thereby be somewhat compromised.
According to this invention, a relatively electrically conductive rubber strip is extended from an electrically conductive tread base layer rubber composition through an electrically resistive tread cap rubber composition where at least a portion of said rubber strip is of a wave configured shape of, for example, a substantially sinusoidal, cycloid al or zigzag form or combination thereof instead of being of a continuous straight line shape. By the term “sinusoidal” it meant that the shape, while approximating a substantial sinusoidal form may somewhat approximate other repetitive patterns so long as the rubber strip is of a wave configured shape composed of at least half of an undulation and preferably at least one and more preferably at least two undulations.
Accordingly, it is one aspect of this invention to provide a tire tread of a cap/base construction having an electrically conductive path extending through the electrically nonconductive tread cap where the electrically conductive path is provided by an electrically conductive rubber strip which exhibits a wave configured shape which may be, for example, of a substantially sinusoidal, cycloid al or zigzag form, or combination thereof, to thereby create a self-locking mechanical configuration between tread segments, particularly tread cap segments, or tread blocks, which are separated by the electrically conductive strip to aid in preserving the lateral stability of the tread cap layer.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, are used interchangeably, unless otherwise indicated. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.
In the description of this invention, the term “phr” refers to parts of a respective material per 100 parts by weight of rubber, or elastomer.